The present invention relates to automatic feeding of carton blanks on container production equipment, and in particular, to an adjustable, versatile feeder for feeding or shingling carton blanks from the top of a stack.
In the manufacture of carton blanks, the need often arises to feed carton blanks from a stack in preparation for the next step. For example, it is sometimes necessary to invert carton blanks in preparation for another operation, or to produce an even stream of carton blanks for infeed to other equipment.
Carton blanks may be fed from the bottom or the top of a stack to form a stream or shingled stream, as the application requires. Separate problems are presented when feeding carton blanks from the bottom or the top, and the present invention concerns the latter. Moving continuous belts have long been used to feed or peel off carton blanks from the top of stacks by frictional contact with the belt. Both the pressure applied to the top blank, and the coefficient of friction between adjacent carton blanks, will effect the feeding of blanks from the stack. As carton blanks are removed, stack height is typically adjusted to return the top blank to a predetermined level.
Because carton blanks are fed by friction, the pressure between the top of the stack and the belt affects the consistency of feeding. Variation in pressure, and thus inconsistent feeding, often results from imprecise control over the belt or pressure-applying means associated with the belt, or by variations in stack height adjustment. As well, inconsistent feeding may result from changeover to different carton blanks, which changes the coefficient of friction between carton blanks and the belt and between adjacent container blanks in the stack. Inconsistent feeding also may be induced by the speed at which the feeder is operated. As a result, carton blanks are fed irregularly, misfed in multiples, and otherwise shingled in an undesirable stream of carton blanks which causes surges and gaps at the infeed of downstream equipment. The resulting variation in stack height at the feeder may also result in a cycle of overcorrection, pressure variation, and continued misfeeding.
In an attempt to provide even feeding, Stobb, U.S. Pat. No. 3,635,463, discloses a sheet feeder for feeding sheets in shingled form from the top of a first stack to the bottom of a second stack. A sensor in contact with the top sheet of the first stack is used to control the position of the first stack at a desired level. A continuous belt in contact with the top sheet of the first stack is mounted on a frame including a rocker arm which pivots about a pin to apply pressure to the back of the continuous belt. A tension spring connected between one end of the rocker arm and a fixed support, urges the rocker arm to pivot downward to apply pressure with the other end to the back of the continuous belt, and thereby feed sheets. The device of Stobb does not work, however, to provide consistent pressure to shingle carton blanks. As the top of the stack varies in height, the rocker arm pivots downward to bring the continuous belt into contact with the top of the stack. The opposite end of the pivot arm moves upward, shortening the tension spring. Because the pressure applied by a spring varies with displacement, the pressure exerted by the spring changes and decreases, varying the pressure applied to the top of the stack and permitting inconsistent feeding to result.
Accordingly, the need exists for more precise, controllable means for feeding which produce a controlled, consistent stream of carton blanks for use in container production equipment. The need further exists for adjustable means for feeding carton blanks to accommodate the use of carton blanks having different coefficients of friction in the same production equipment.